1. Technical Field
The present invention relates to storage area networks and, in particular, to multiple path input/output environments. Still more particularly, the present invention provides a method, system, and program for maintaining and swapping paths in a multiple input/output environment.
2. Description of Related Art
A storage area network (SAN) is a network of storage devices. In large enterprises, a SAN connects multiple machines to a centralized pool of disk storage. Compared to managing hundreds of servers, each with their own storage devices, a SAN improves system administration.
In multiple path input/output (MPIO), there is a plurality of routes or connections from one specific machine to one specific device. For example, with a logical disk device on a redundant array of independent disks (RAID), the accessing host uses a fibre channel (FC) adapter connected to an FC switch, and the FC switch in turn is attached to the RAID array. There may be eight, or as many as thirty-two or more, FC adapters in both the host and the device.
Considering a SAN with eight adapters in the host and the device, if each host adapter is connected to a device adapter through a switch, then there may be eight paths from the host to the device. If the switches are interconnected, then there may be many more paths from the host to the device.
All of the MPIO solutions today use a simple round robin among all of the available paths. When a path fails, it is removed from the round robin until the failed element is restored. This approach does not provide much load balancing among the physical resources in the SAN, e.g., the FC switches. In other words, paths in the round robin may be using the same resources.
Therefore, it would be advantageous to provide an improved mechanism for load balancing and failover for paths in an MPIO environment.